Tire noise reducing system

ABSTRACT

A tire noise reducing system comprises a pneumatic tire, a wheel rim and a noise damper disposed in a cavity formed between the rim and tire when mounted as being surrounded by the tire and rim, the noise damper is made of a porous material having a specific gravity of from 0.005 to 0.06 and secured on a surface facing the cavity, the volume S 2  of the noise damper is in a range of from 0.4 to 20.0% of the volume S 1  of the cavity. Preferably, the noise damper is provided with an uneven surface or an outer layer for less sound reflection, and the shape index E of the noise damper is more than 1, and the ratio T/W of the thickness T to the width W of the damper is not less than 1.

FIELD OF INVENTION

The present invention relates to a tire noise reducing system, moreparticularly to a noise damper which is disposed on a pneumatic tire orwheel rim facing the tire cavity.

DESCRIPTION OF RELATED ART

As is well known, when a pneumatic tire is mounted on a wheel rim, thetire hollow forms a closed annular cavity filled with air. Duringrunning the air is excited by vibrations and resonance is caused atspecific frequencies depending on the size of the cavity. Such resonanceworsens the running noise from the tire.

It was known that such a resonance noise can be reduced by putting asponge-like material into the cavity. However, if a big damper is usedin order to completely reduce the resonance noise, even if the damper ismade of a light sponge-like material, the wheel is liable to lose itsrotational balance. This is particularly remarkable when the dampercontacts with the tire inside.

BRIEF SUMMARY OF THE INVENTION

It is therefore, an object of the present invention to provide a noisereducing system including a noise damper being capable of achieving amaximum noise reduction with a minimum damper size.

According to one aspect of the present invention, a tire noise reducingsystem includes:

a pneumatic tire,

a wheel rim on which the pneumatic tire is mounted, and

a noise damper disposed in a cavity, the cavity formed between the rimand tire when mounted as being surrounded by the tire and rim,

the noise damper being made of a porous material having a specificgravity of from 0.005 to 0.06 and secured on a surface facing thecavity,

and the volume S2 of the noise damper being in a range of from 0.4 to20.0% of the volume S1 of the cavity.

Preferably, the noise damper is provided with an uneven surface or anouter layer for less sound reflection facing the cavity. Theundermentioned shape index E of the noise damper is more than 1, and theratio T/W of the thickness T to the width W of the damper is not lessthan 1.

BRIEF DESCRIPTION OF DRAWINGS

Embodiments of the present invention will now be described in detail inconjunction with the accompanying drawings.

FIG. 1 is a cross sectional view of a tire and rim assembly showing anembodiment of the present invention.

FIG. 2 is a perspective view of an example of the noise damper having alayered structure.

FIGS. 3-8 are perspective views showing various examples of the unevenface optionally provided on the noise damper.

FIG. 9 is a cross sectional view of a tire and rim assembly showinganother example of the cross sectional shape of the noise damper.

FIGS. 10a, 10 b, 10 c, 10 d and 10 e each show another example of thecross sectional shape of the noise damper.

FIG. 11 is a cross sectional view of a tire and rim assembly showinganother embodiment of the present invention.

FIG. 12 is a developed view showing the wheel rim thereof.

FIGS. 13-16 are developed views each showing another example of thewheel rim.

FIG. 17 is a graph showing a relationship between the volume ratio S2/S1and noise.

FIG. 18 is a graph showing a relationship between the shape index E andnoise.

DETAILED DESCRIPTION OF INVENTION

According to the present invention, a tire noise reducing systemincludes a pneumatic tire 2 with a wheel centerline C, a wheel rim 3 onwhich the tire 2 is mounted and a noise damper 5 disposed in a cavity 4,wherein the cavity 4 is defined as being surrounded by the pneumatictire 2 and wheel rim 3 when the pneumatic tire 2 is mounted on the wheelrim 3.

The pneumatic tire 2 is a tubeless tire comprising a tread portion 2 t,a pair of bead portions 2 b and a pair of sidewall portions extendingtherebetween. The inside facing the cavity 4 is covered with an innerliner made of air-impermeable rubber.

The wheel rim 3 comprises a pair of bead seats 3 s, a pair of flanges 3f each extending radially outwardly from one of the bead seats 3 s and awell 3 w between the bead seats for tire mounting.

The noise damper 5 is made of at least one kind of porous materialhaving a specific gravity in a range of from 0.005 to 0.06, preferably0.010 to 0.05, more preferably 0.016 to 0.05, still more preferably0.016 to 0.035.

Here, the porous material means not only a foamed elastomer or plasticof an open-cell or closed-cell type but also shaped intertangled fibersuch as synthetic fiber, plant fiber and animal fiber. In theunder-mentioned examples, open-cell type poly-urethane foam is used.

The volume S2 of the noise damper 5 should be at least 0.004 times thevolume S1 of the cavity 4. Preferably, the volume S2 is set in a rangeof not less than 0.01 times, more preferably not less than 0.02 times,still more preferably not less than 0.04 times, but not more than 0.2times the volume S1.

Here, the volume S1 of the cavity 4 is defined under the normal inflatedcondition by the following approximate equation:

S 1 =A×{(Di−Dr)/2+Dr}×pi

wherein

“A” is the cross sectional area of the cavity 4,

“Di” is the maximum outer diameter of the cavity 4, and

“Dr” is the wheel rim diameter.

The above-mentioned normal inflated condition is such that the tire 2 ismounted on the wheel rim 3 and inflated to a standard pressure butloaded with no tire load. The standard pressure is the “maximum airpressure” in JATMA, the “Inflation Pressure” in ETRTO, the maximumpressure given in the “Tire Load Limits at Various Cold InflationPressures” table in T&RA or the like. In case of passenger car tires,however, 200 kPa is used as the standard pressure. The under-mentionedtread width is the maximum axial width of the ground contacting regionunder a standard loaded condition. The standard loaded condition is suchthat the tire is mounted on the wheel rim and inflated to the standardpressure and then loaded with a standard load, wherein the standard loadis the “maximum load capacity” in JATMA, the “Load capacity” in ETRTO,the maximum value given in the above-mentioned table in TRA or the like.

FIG. 17 shows results of an inventors' test in which a resonance noisewas measured changing the damper volume S2. As apparent from thisfigure, the resonance noise is correlative with the ratio S2/S1. Byincreasing the ratio S2/S1 over 0.004, the resonance noise can beeffectively reduced. But, even if the ratio S2/S1 is increased over 0.2,a further reduction can not be expected or rather the tire weight isunfavorably increased so that the wheel is liable to get off rotationalbalance.

FIGS. 1 and 9 show embodiments in which the noise damper 5 is fixed tothe pneumatic tire 2.

FIGS. 11-16 show embodiments in which the noise damper 5 is fixed to thewheel rim 3.

Pneumatic Tire with Noise Damper

FIG. 1 shows an example of the pneumatic tire 2 in which the noisedamper 5 is fixed to the reverse face of the tread 2 tusing an adhesiveagent. For the adhesive agent, a synthetic-rubber-based adhesive ispreferably used.

As the synthetic-rubber-based adhesive, synthetic rubber dissolved by anorganic solvent (solvent type) and synthetic rubber dispersed in water(colloidal type) can be used. Especially, chloroprene rubber dissolvedby an organic solvent is preferably used because of adhesive strength,elasticity and the like. As the organic solvent, cyclohexane, acetoneand hexane are preferably used alone or in combination. The content ofthe chloroprene rubber is set in a range of from 25 to 35 parts byweight on the basis of the entirety of the synthetic-rubber-basedadhesive 9 being 100 parts by weight. If less than 25 parts by weight,it is difficult to obtain a necessary adhesive strength. If more than 35parts by weight, it becomes difficult to apply the adhesive because oftoo much viscosity.

In general, the inside of a vulcanized tire is covered with a moldrelease agent such as silicone oil and the like. In case ofsynthetic-rubber-based adhesive, the adhesive strength is decreased bysuch a mold release agent and the noise damper 5 is liable to come offduring use especially during high speed running. Accordingly, the moldrelease agent must be removed from the tire inside before applying theadhesive agent. However, if an organic solvent is used, the inner linerrubber is liable to be changed in quality. Therefore, buffing ispreferably employed.

By applying a synthetic-rubber-based adhesive to all over or spots of abuffed face, the noise damper 5 is fixed to the tire inside 4 s.

In FIG. 1, the noise damper 5 is made of one kind of open-cell typepoly-urethane foam. In this case, it is preferable that the volume ratioS2/S1 is at most 0.1. The circumferential length of the noise damper 5is at least 20 mm, and the width W is set in a range of from 20 mm tothe above-mentioned tread width plus 40 mm. The thickness T is set in arange of from 3.0 mm to 80% of the section height of the cavity 4. Thesection height is measured under the above-mentioned normal inflatedcondition.

This example is a single layer of a porous material. But, it is alsopossible that the noise damper 5 is formed of plural layers of porousmaterials.

Layered Structure

FIG. 2 shows the noise damper 5 having a double layered structure whichcomprises an outer layer 5B made of a porous material whose soundreflection coefficient is lower and an inner layer 5A made of a porousmaterial whose sound absorption factor is higher.

In this example, two kinds of open-cell type poly-urethane foam are usedfor the inner layer 5A and outer layer 5B. The expansion ratio thereofis greatly increased in the outer layer 5B in comparison with the innerlayer 5A so as to decrease the ratio α2/α1 of the specific gravity α2 ofthe outer layer 5B to the specific gravity al of the inner layer 5A in arange of not more than 0.7, preferably not more than 0.5. The thickness(t) of the outer layer 5B is preferably set in a range of from 0.05 to0.3 times the overall thickness T of the noise damper 5.

Such a layered structure can be made using an adhesive agent. In thiscase, however, if the adhesive agent is applied to a wide area, suchportion is liable to reflect sound wave to decrease the noise dampingeffect. Thus, it is preferable that the adhesive-agent-applied area Scis not more than 0.05 times the whole area Sa.

In addition to the method bonding two layers 5A and 5B together, thelayered structure can be made by another way, for example, changing theexpansion ratio during foaming the materials, namely, a materialincluding a foaming agent for a higher expansion ratio and a materialincluding a foaming agent for a lower expansion ratio are put togetherand then the agents are foamed. In this case, the layers 5A and 5B areformed integrally with each other and the expansion ratio may begradually changed in the neighborhood of their boundary. Accordingly,sound wavy reflection from the boundary portion may be effectivelyreduced.

As described above, an expanded elastomer is preferably used in theinner layer 5A and outer layer 5B. But, other materials such as glasswool, felt and the like may be used in the outer layer 5B.

In the example shown in FIG. 1, the cross sectional shape of the noisedamper 5 is flat, namely, the width is larger than the thickness T. Itis effective in reducing the noise to lessen the sound wave reflectionfrom the noise damper 5. The above-mentioned double-layered structurecan lessen the sound wave reflection by its outer layer 5B whileabsorbing the incident wave thereon by its inner layer 5A.

Uneven Face

It is also effective in attenuating the sound wave traveling along asurface. Thus, the surface 5S of the noise damper 5 facing the cavity 4is preferably formed as a patterned uneven face 10.

The roughness h2 of the uneven face 10 or the distance measured betweentop and bottom in the height direction or depth direction is preferablyset in a range of not less than 5 mm, more preferably not less than 10mm.

FIG. 3 shows an example of the uneven face 10 which is formed by concave10A and convex 10B smoothly joined together, and the entirety thereof iscurved or undulated and there is no flat part. FIG. 4 shows anotherexample of the uneven face 10 which is formed by making convexprotrusions 10B in a flat face part 11. FIG. 5 shows another example ofthe uneven face 10 which is formed by making concave holes 10A in a flatface part 11.

FIGS. 6-8 show other examples of the uneven face 10 formed by usinggrooves 10A or ridges 10B extending crosswise to the circumferentialdirection. In FIG. 6, the uneven face 10 is formed by parallel ridges10B in a flat part 11. In FIG. 7, the uneven face 10 is formed byparallel grooves 10A in a flat part 11. In FIG. 8, the uneven face 10has not a flat part 11.

As to the sizes, shapes and formation of the holes/grooves 10A andprotrusions/ridges 10B, they are formed regularly in the above-mentionedexamples and arranged at regular pitches h3 with respect to a direction,but it is also possible to make them irregularly.

In the uneven face 10 of the noise damper 5, the ratio Sb/Sa of theactual surface area Sb to the projected area Sa on the assumption thatthere is no uneven surface is preferably set in a range of from 1.04 to5.00.

The uneven face 10 can be provided irrespective of whether the noisedamper 5 is single layered or double layered.

Comparison Test 1

The following noise test was conducted using a wheel rim of size 15×6JJand radial tires of size 195/65R15 shown in FIG. 1 and various noisedampers shown in Table 1.

1) Noise Test

A Japanese 2000cc FF car provided on all of the four wheels withtire/rim assembly was coasted on a rough asphalt road surface in a noisetest course (speed=60 km/hr, tire pressure=200 kPa), and the noise soundwas measured at the front seat and analyzed to obtain a peak of thesound pressure level near 245 Hz caused by the resonance of air in thecaivity. The sound pressure level at the peak in dB(A) is indicated as adifference from Ref. 1.

Test results and the specifications of the dampers are shown in Table 1.

TABLE 1 Tire Ref.1 Ref.2 Ex.1 Ex.2 Ref.3 Ex.3 Ex.4 Ex.5 Ex.6 Ex.7 Dampernone S2/S1 (%) 0 5.4 5.4 5.4 6.8 6.8 6.8 6.8 6.8 6.8 S2 (cu.cm) 0 16471647 1647 2059 2059 2059 2059 2059 2059 Thickness T (mm) 0 10 10 10 12.520 20 20 20 20 Width W (mm) 0 90 90 90 90 90 90 90 90 90 Length L (mm) 01830 1830 1830 1830 1830 1830 1830 1830 1830 Surface — even unevenuneven even uneven uneven uneven uneven uneven FIG. 5 FIG. 2 FIG. 8 FIG.8 FIG. 8 FIG. 8 FIG. 8 h2 (mm) — — irregular 8 — 15 15 15 15 15 h3 (mm)— — irregular 32 — 4 6 10 40 80 Sb/Sa 0 1 1.02 1.45 1 7.57 5.1 3.16 1.251.07 Layer 1 1 1 1 1 1 1 1 1 1 α2/ α1 — — — — — — — — — — t/T — — — — —— — — — — Sc/Sa — — — — — — — — — — Test result Noise (dB) 0 −3.9 −4.3−4.4 −4.6 −7.6 −7.5 −6.7 −5.9 −5.5 Tire Ex.8 Ex.9 Ex.10 Ex.11 Ex.12Ex.13 Ex.14 Ex.15 Ex.16 Damper S2/S1 (%) 6.8 6.8 6.8 6.8 6.8 5.4 5.4 5.45.4 S2 (cu.cm) 2059 2059 2059 2059 2059 1647 1647 1647 1647 Thickness T(mm) 20 20 20 20 20 10 10 10 10 Width W (mm) 90 90 90 90 90 90 90 90 90Length L (mm) 1830 1830 1830 1830 1830 1830 1830 1830 1830 Surfaceuneven uneven uneven uneven uneven even even even uneven FIG. 8 FIG. 8FIG. 8 FIG. 8 FIG. 8 FIG. 5 h2 (mm) 15 15 15 15 15 — — — irregular h3(mm) 100 120 140 160 200 — — — irregular Sb/Sa 1.04 1.031 1.023 1.0171.011 1 1 1 1.02 Layer 1 1 1 1 1 2 2 2 α2/α1 — — — — — 0.5 0.5 0.5 0.5t/T — — — — — 0.2 0.2 0.2 0.2 Sc/Sa — — — — — 100% 5% 0% 0% Test resultNoise (dB) −5.2 −5 −4.8 −4.7 −4.6 −4 −4.6 −5 −5.5

In Ex.1 to Ex.12 and Ref.2 and 3, the dampers had a single-layeredstructure of open-cell type poly-urethane foam having a specific gravityof 0.022. Ex.13 to Ex.16 had a double-layered structure of the innerlayer made of open-cell type poly-urethane foam having a specificgravity of 0.022 and the outer layer made of open-cell typepoly-urethane foam having a specific gravity of 0.010.

As known from a comparison between Ref.1 and Ref.2 & 3, even when thedamper had an even surface, the noise could be reduced 3.9 to 4.6 dB. Byusing the damper provided with the uneven face, the noise was furtherreduced as apparent from a comparison between Ref.2 and Ex.1 & 2 and acomparison between Ref.3 and Ex.3 to 12. Especially, as shown by Ex.3 toEx.12, the noise reduction by the uneven face becomes displayed when theratio Sb/Sa exceeds 1.04. Further, as known from a comparison betweenRef.2 and Ex.13 to Ex.16, by using the double layered structure, a noisereduction as the same level as that by the uneven face could beobtained. Further, as apparent from Ex.13 to Ex.15, as the adhesiveagent applied area became smaller, the noise was improved. By employingboth the uneven face and double layered structure, the noise can befurther improved.

Comparison Test 2

Further, the following high-speed durability test was conducted togetherwith the above-mentioned noise test using a wheel rim of size 15×6JJ andradial tires of size 195/65R15 shown in FIG. 1 and noise dampers of asingle layered structure of open cell type poly-ulethan foam having aspecific gravity of 0.022.

2) High-speed Durability Test

Using a tire test drum, a cyclic test, which repeats running for 20minutes at a speed, checking the noise damper for damage, increasing thespeed by a step of 10 km/hr from 120 km/hr to 250 km/hr, was made undera tire pressure of 280 kPa and tire load of 4.83 kN, until the noisedamper was broken or the speed reached to 250 km/hr without broken.

Test results and the specifications of the dampers are shown in Table 2.

TABLE 2 Tire Ref.1 Ref.2 Ex.1 Ex.2 Ex.3 Ex.4 Ex.5 Damper none S2/S1 (%)0 5.4 5.4 5.4 5.4 5.4 5.4 Volume S2 (cu.cm) 0 1647 1647 1647 1647 16471647 Thickness T (mm) — 10 10 10 10 10 10 Width W (mm) — 90 90 90 90 9090 Length L (mm) — 1830 1830 1830 1830 1830 1830 Surface — even eveneven even uneven uneven FIG. 5 FIG. 8 h2 (mm) — — — — — irregular 8 h3(mm) — — — — — irregular 32 Sb/Sa — 1 1 1 1 1.02 1.45 fixee ?*1 — no yesyes yes yes yes Application — — spot spot all over all over all overBuffed ? — — no yes yes yes yes Test Results Noise (dB) 0 −4.9 −4.2 −4.2−3.9 −4.3 −4.4 High-speed durability (km/hr) — 160 160 250 250 250 250Damper broken ? yes yes no no no no *1) In order to fix the damper tothe tire inside, a synthetic-rubber-based adhesive (chloroprene rubber =30%, cyclohexane + acetone + hexane = 70%) was used.

In Ref.2 after the damper was broken at 160 km/hr, the noise wasincreased from −4.9 dB to −0.7 dB. In Ex.2 and Ex.3, the noise reducingeffect was slightly low in comparison with Ref.2, but it could bemaintained up to 250 km/hr. In Ex.1, as the tire inside was not buffed,the damper was separated at 120 km/hr and broken at 160 km/hr. In Ex.4and Ex.5, as the damper surface was made uneven, the noise was furtherimproved.

Radially Oblong Cross Sectional Shape

FIG. 9 shows another example of the noise damper 5 which has a radiallyoblong cross sectional shape in which the thickness T is larger than thewidth W.

When the pneumatic tire 2 is a low-aspect tire or a wide tread tirewhich are widely used nowadays, it is effective in controlling the airresonance of the cavity 4 to divide the width of the cavity 4 in two.

FIG. 18 shows results of a multi-regression analysis of the airresonance noise level and the size (width W, thickness T and length L)of the noise damper 5. From the results, it was discovered that if ashape index E is defined by the following equation

E=0.42+0.45×(W×T×L/S 1×100)+1.11×(T/W)

then noise reduction in dB becomes in direct proportion to the shapeindex E with the proportionality constant being 1. For example, if theshape index E is 1, the noise reduction becomes about 1 dB. Thus, theresonance noise reduces as the shape index E increases. As the noisereduction can be realized when it exceeds about 2 dB, the shape index Eshould be set in a range of not less than 2, preferably not less than 5.

The value “W×T×L” in the second term corresponds to the volume S2 of thenoise damper 5. Therefor, the contribution of the volume S2 to the noisereduction is 0.45 (45%) whereas the value “T/W” in the third term is1.11 (111%). Accordingly, it is more effective in increasing the shapeindex E or reducing the noise to adjust the thickness/width ratio T/Wrather than the volume S2. By properly selecting a value for thethickness/width T/W, the same noise reduction may be obtained whiledecreasing the volume S2.

From this point of view, the T/W ratio is preferably set in a range ofnot less than 0.5, more preferably not less than 1.0 but preferably notmore than 3.0.

As shown in FIGS. 9 and 10a-10 e, the noise damper 5 oblong in the tireradial direction may have various cross sectional shapes such as arectangle (FIG. 9), triangle or V-shape (FIG. 10a), U-shape (FIG. 10b),trapezoidal (FIGS. 10c, 10 d), conventional-keyhole shape (FIG. 10e) andthe like.

In the examples shown in FIGS. 9 and 10a-10 e, open-cell typepoly-urethane foam having a specific gravity of from 0.005 to 0.06,preferably 0.010 to 0.05, more preferably 0.016 to 0.05, still morepreferably 0.016 to 0.035 is used. In the radially oblong noise damper 5too, it is possible to provide the surface 5S facing the cavity 4 withthe above-mentioned uneven face 10. Further, it is possible to providethe noise damper 5 with the above-mentioned double layered structure. Inthis case, it is preferable that the outer layer 5B is formed along theentire surface as shown in FIGS. 10a-10 e by a broken line.

It is possible to make a flame proof finish on the noise damper 5 byapplying a flame retardant.

Comparison Test 3

Using a wheel rim of size 16×6.5JJ and radial tires of size 215/60R16shown in FIG. 9, and radially oblong noise dampers having a singlelayered structure of open-cell type poly-urethane foam having a specificgravity of 0.02, the following noise test was conducted.

3) Noise Test

A Japanese 2300cc FF car provided on all of the four wheels withtire/rim assembly was coasted on a rough asphalt road surface in a noisetest course (speed=60 km/hr, tire pressure=200 kpa), and the noise soundwas measured at the front seat and analyzed to obtain a peak of thesound pressure level near 230 Hz caused by resonance. In Table 1, thesound pressure level at the peak in dB(A) is indicated as a differencefrom Ref.

Test results and the specifications of the dampers are shown in Table 3.

TABLE 3 Tire Ref. Ex.1 Ex.2 Ex.3 Ex.4 Ex.5 Ex.6 Ex.7 Ex.8 Damper noneShape — FIG. 9 FIG. 9 FIG. 9 FIG. 9 FIG. 9 FIG. 9 FIG. 9 FIG. 9 Width W(mm) — 10 10 10 10 4 2 4 2 Thickness T (mm) — 1 2 3 4 2.5 5 5 10 LengthL (mm) — 183 183 183 183 183 183 183 183 T/W — 0.1 0.2 0.3 0.4 0.625 2.51.25 5 S2/S1*1 (%) — 4.9 9.8 14.7 19.6 4.9 4.9 9.8 9.8 Shape index E —2.7 5.1 7.4 9.7 3.3 5.4 6.2 10.4 Test Result Noise (dB) 0 −2.9 −4.4 −6.1−10.5 −4.1 −5.6 −6.8 −10 Tire Ex.9 Ex.10 Ex.11 Ex.12 Ex.13 Ex.14 Ex.15Damper Shape FIG. 9 FIG. 9 FIG. 10a FIG. 10c FIG. 10e FIG. 10b FIG. 10dWidth W (mm) 4 3 4 5 3.6 4 5 Thickness T (mm) 7.5 10 7 5 6.8 6 5 LengthL (mm) 183 183 183 183 183 183 183 T/W 1.875 3.3 1.75 1 1.89 1.5 1S2/S1*1 (%) 14.7 14.7 6.9 9.8 8.2 10.9 9.8 Shape index E 9.1 10.7 5.55.9 6.2 7 5.9 Test Result Noise (dB) −8.7 −10.8 −6.8 −7.3 −6.9 −7 −6.8*1) Cavity volume S1 = 3.73 × 10⁴ cu.cm

Wheel Rim with Noise Damper

FIGS. 11-16 show embodiments in which the noise damper 5 is fixed to thewheel rim 3.

The wheel rim 3 used in the above-mentioned embodiments are aconventional or ordinary wheel rim. The noise damper 5 in the presentinvention can be used in combination with such a conventional rim. But,when the noise damper 5 is fixed to the wheel rim 3, it is preferablethat the wheel rim 3 is provided with a shelter groove 9 to prevent thenoise damper 5 from being damaged by the tire beads 2 b during mountingthe tire on the rim. Incidentally, the wheel rim 3 can be formedintegrally with a disk portion 3 d for attachment to a vehicle axis.But, it is also possible to make the wheel rim 3 and disk portion 3 dseparately and then fixed to each other.

The shelter groove 9 is formed within the rim well 3 w. Preferably, thegroove depth T2 is set in a range of not more than 20 mm, and the groovewidth W2 is set in a range of not more than 60 mm. The shelter groove 9is provided with a cross sectional shape adapted to that of the noisedamper 5. The entirety or major part of the noise damper 5 is put in theshelter groove 9.

Usually, the shelter groove 9 extends continuously in thecircumferential direction, but it can be discontinuous at one or morecircumferential positions.

In the example shown in FIG. 12, the shelter groove 9 extends straight.But, the example shown in FIG. 13 extends zigzag in the circumferentialdirection. In case of zigzag groove, the peak-to-peak amplitude H1 ofeach groove edge is preferably set in a range of from 0.3 to 1.0 timesthe groove width W2 in the axial direction. Preferably, the number N ofthe zigzag cycles around the rim well 3 w is set in a range of from 4 to20. Therefore, the protruding parts of the zigzag groove edges towardsthe groove can prevent the tire beads from falling into the sheltergroove 9 during mounting the tire on the rim.

FIG. 14 shows another example of the shelter groove 9. This example isstraight, but piers 20 protruding into the groove from at least one ofthe groove walls are provided in order to prevent tire beads fallinginto the groove 9. In this case, the noise damper 5 may be provided withcuts 21 to clear the piers 20. In the example shown in FIG. 14, thepiers 20 are staggeringly disposed on both the groove walls, and theprotrusion H2 of each pier 20 in the axial direction is set in a rangeof not less than 0.3 times, preferably not less than 0.5 times thegroove width W2. The piers 20 can be extend to the groove bottom. Theupper faces of the piers 20 are at the same level as the bottom of therim well 3 w, and the axial ends of the piers 20 are rounded by a radiusof about 2.0 mm to prevent the tire beads from getting scratched.

In the above-mentioned examples, the noise damper 5 is preferably fixedto the bottom of the shelter groove 9 by using the adhesive agent.

In case the noise damper 5 protrudes from the bottom of the rim well 3w, it is preferable that the protrusion H is limited in a range of notmore than 15 mm from the bottom level of the rim well 3 w. Theprotruding part of the noise damper 5 can be formed as theabove-mentioned uneven face 10 and/or outer layer 5B.

Protector

FIGS. 15 and 16 show protectors 22 for the noise damper 5. In contrastto the above-mentioned piers 20 which are formed integrally with the rimmain, the protectors 22 are separate, but it has the same purpose,namely, to protect the noise damper 5 from tire beads during tiremounting.

The protector 22 is a mesh-like structure which comprisescircumferentially extending side frames 22 s fixed to both sides of theshelter groove 9, and crossbars 22 c extending between the side frames22 s.

In FIG. 15, the crossbars 22 c are formed integrally with the sideframes 22 s using a rigid material such as metallic material andplastics material.

In FIG. 16, the crossbars 22 c are formed in a form of cross meshseparately from the side frames 22 s using a material different from theside frames.

Thus, the noise damper 5 is prevented from being took out from theshelter groove 9 and being torn off by tire beads 2 b at the time oftire mounting. Also the tire beads 2 b are prevented from falling intothe shelter groove 9.

The noise damper 5 is pushed into the shelter groove 9 and then theprotector 22 is fixed. As a result, due to the sponge-like elasticity ofthe noise damper 5, part of the noise damper 5 adjacent to the surface5S protrudes through the meshes and thereby uneven face 10 having thesame pattern as the meshes is formed. The size of the meshes isdetermined accordingly.

Comparison Test 4

The following tire mounting test and noise test were conducted using aradial tire of size 165/65R15, wheel rims of size 15×5J having the samestructure shown in FIG. 11 except for the shelter groove 9 and protector22, and noise dampers 5 made of open-cell type poly-urethane foam havinga specific gravity of 0.022.

Test results and the specifications of the wheel rims and dampers areshown in Table 4.

4) Mounting Test

The workability when mounting the tire on the wheel rim was evaluatedinto five ranks based on Ref.1 being 5, wherein the larger the ranknumber, the better the workability.

5) Noise Test

A Japanese 1500 cc hybrid car provided on all of the four wheels withtire/rim assembly was coasted on a rough asphalt road surface in a noisetest course (speed=60 km/hr, tire pressure=200 kPa), and the noise soundwas measured at the front seat and analyzed to obtain a peak of thesound pressure level near 248 Hz caused by resonance. In Table 4, thesound pressure level at the peak in dB(A) is indicated as a differencefrom Ref.1.

TABLE 4 Wheel Rim Ref.1 Ref.2 Ex.1 Ex.2 Ex.3 Ex.4 Ex.5 Ex.6 Ex.7 Sheltergroove none none FIG. 12 FIG. 12 FIG. 12 FIG. 13 FIG. 14 FIG. 15 FIG. 16Piers — — — — — — FIG. 14 — — Protector — — — — — — — FIG. 15 FIG. 16Damper none Volume S2 (cu.cm) 0 446 208 104 416 208 208 416 416Thickness T (mm) 0 10 10 5 10 10 10 10 10 Width W (mm) 0 40 20 20 40 2020 40 40 Length L (mm) 0 1115 1040 1040 1040 1040 1040 1040 1040 S2/S1*1(%) 0 2.24 1.04 0.52 2.09 1.04 1.04 2.09 2.09 Test results Mounting 5 13 3 3 4 4 5 5 Noise (dB) 0 −4.4 −2.7 −1.2 −4 −2.8 −2.6 −3.7 −3.8 *1)Cavity: Volume S1 = 1.99 × 10⁴ cu.cm, Cross sectional area A = 134.64sq.cm

What is claimed is:
 1. A tire noise reducing system comprising: apneumatic tire, a wheel rim on which the pneumatic tire is mounted, anda noise damper disposed in a cavity surrounded by an inner surface ofthe rim and an inner surface of the tire mounted thereon, the noisedamper being made of a porous material having a specific gravity of from0.005 to 0.06 and secured on the inner surface of the tire, facing theinterior of the cavity, the volume S2 of the noise damper being in arange of from 0.4 to 20.0% of the volume S1 of the cavity.
 2. A tirenoise reducing system according to claim 1, wherein the noise damper isprovided with a layered structure comprising an outer layer for lesssound reflection facing the cavity and an inner layer for soundabsorption.
 3. A tire noise reducing system according to claim 1,wherein the noise damper is provided with an uneven surface facing thecavity.
 4. A tire noise reducing system according to claim 2, whereinthe outer layer is provided with an uneven surface facing the cavity. 5.A tire noise reducing system according to claim 1, wherein the noisedamper has a width W in the tire axial direction; a thickness T in thetire radial direction; and a length L in the tire circumferentialdirection which satisfy the following condition:0.42+0.45×(W×T×L/S1×100)+1.11×(T/W)>1.
 6. A tire noise reducing systemaccording to claim 5, wherein wherein the width W, the thickness T andthe length L satisfy the following condition:0.42+0.45×(W×T×L/S1×100)+1.11×(T/W)>2.
 7. A tire noise reducing systemaccording to claim 5 or 6, wherein the ratio T/W of the thickness T tothe width W is not less than
 1. 8. A tire noise reducing systemaccording to claim 1, wherein the noise damper is secured to the innersurface of the tread of the pneumatic tire.
 9. A tire noise reducingsystem according to claim 8, wherein the noise damper is fixed to abuffed inner surface of the tread by a synthetic-rubber-based adhesive.10. A tire noise reducing system according to claim 9, wherein thesynthetic-rubber-based adhesive includes chloroprene rubber dissolved byan organic solvent.
 11. A pneumatic tire comprising: a tread portion, apair of bead portions, a pair of sidewall portions extendingtherebetween, and a noise damper fixed to the inner surface of the treadand made of a porous material having a specific gravity of from 0.005 to0.06, the noise damper provided with a layered structure comprising anouter layer for less sound reflection facing the tire cavity and aninner layer for sound absorption.
 12. A pneumatic tire comprising: atread portion, a pair of bead portions, a pair of sidewall portionsextending therebetween, and a noise damper fixed to the inner surface ofthe tread and made of a porous material having a specific gravity offrom 0.005 to 0.06, the noise damper provided with an uneven surfacefacing the tire cavity.
 13. A pneumatic tire according to claim 11 or12, wherein the noise damper has a width W in the tire axial direction;a thickness T in the tire radial direction; and a length L in the tirecircumferential direction which satisfy the following condition:0.42+0.45×(W×T×L/S1×100)+1.11×(T/W)>1.
 14. A pneumatic tire according toclaim 11 or 12, wherein the noise damper has a width W in the tire axialdirection; a thickness T in the tire radial direction; and a length L inthe tire circumferential direction which satisfy the followingcondition: 0.42+0.45×(W×T×L/S1×100)+1.11×(T/W)>1 and S1 is theabove-mentioned volume of the cavity, and the ratio T/W of the thicknessT to the width W is not less than 1.